• 한국표면공학회지
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• 제5권3호
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• pp.77-85
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• 1972

A method of preparation of synthetic ignorgaic coating on copper (patina) has been presented . An Eh--pH diagram was constructed for the present Cu-H2O-SO$_4$ system using the most recently available thermodynamic data. In the path of the patination at room temperature the general behaviour of copper in acidic copper sulfate solutions with potassium chlorate as an oxidizing agent appeared to follow those predictable in this Eh-pH diagram. In the presence 0.05 molar cupric sulfate at a temperature of about 28$^{\circ}C$ a green brochantite (CuSO$_4$$.$3Cu(OH)$_2$) layer was formed on copper sheet in 20 days. In a solution having an initial pH of 3.5 the development of a brochantite coating has been observed to take place in two stages. In the first, a layer of cuprous oxide formed on the copper at a relatively rapid rate. In the ensuing step the outer layer of cuptrite was oxidized at much slower rate to form brochantite. The syntetic coatings appeared to consist of crystal-lites of brochanitite growing perpendicular to the cuprose oxide surface. The outer tips of the -crystallites were reasily broken off and gave to the layer a rather chalky character. Underneath, at the brochantite Cu$_2$O interface, however, the green layers were firmely attached. The effect of reagent concentration , solution agitation , and moderate temperature increase were investigated to improve the quality of coating. So also in a qualitative way were the effect of light.

• 한국토양비료학회지
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• 제44권2호
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• pp.297-302
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• 2011

Acid drainage generated by pyrite oxidation has caused the acidification of soil and surface water, the heavy metal contamination and the corrosion of structures in abandoned mine and construction sites. The applicability of Na-acetate (Na-OAc) buffer and/or Na-silicate solution was tested for suppressing pyrite oxidation by reacting pyrite containing rock and treating solution and by analyzing solution chemistry after the reaction. A finely ground Mesozoic andesite containing 10.99% of pyrite and four types of reacting solutions were used in the applicability test: 1) $H_2O_2$, 2) $H_2O_2$ and Na-silicate, 3) $H_2O_2$ and 0.01M Na-OAc buffer at pH 6.0, and 4) $H_2O_2$, Na-silicate and 0.01M Na-OAc buffer at pH 6.0. The pH in the solution after the reaction with the andesite sample and the solutions was decreased with increasing the initial $H_2O_2$ concentration but the concentrations of Fe and $SO_4^{2-}$ were increased 10 - 20 times. However, the pH of the solution after the reaction increased and the concentrations of Fe and $SO_4^{2-}$ decreased in the presence of Na-acetate buffer and with increasing Na-silicate concentration at the same $H_2O_2$ concentration. The solution chemistry indicates that Na-OAc buffer and Na-silicate suppress the oxidation of pyrite due to the formation of Fe-hydroxide and Fe-silicate complex and their coating on the pyrite surface. The effect of Na-OAc buffer and Na-silicate on reduction of pyrite oxidation was also confirmed with the surface examination of pyrite using scanning electron microscopy (SEM). The result of this study implies that the treatment of pyrite containing material with the Na-OAc buffer and Na-silicate solution reduces the generation of acid drainage.

• 자원리싸이클링
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• 제13권6호
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• pp.43-48
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• 2004

본 연구는 NdFeB 영구자석 폐 스크랩 분말을 600$^{\circ}C$에서 산화배소한 후, 초산을 사용한 약산침출을 수행하여 네오디뮴을 선택적으로 분리하고자 하였다. 산화배소된 스크랩 분말의 초산침출 결과, 네오디뮴의 침출율 90% 이상을 얻기 위한 조건은 반응온도 80$^{\circ}C$, 반응시간 3시간 그리고 광액농도 35%이었다. 초산 침출용액으로부터 분별결정화에 의한 네오디뮴아세테이트 회수 시, 증발후 여액의 네오디뮴 조성은 243 g/l 네오디뮴아세테이트의 초산에 대한 용해도(260 g/l)에 근접하는 것을 알 수 있으며, 침출용액으로부터 네오디뮴아세테이트 결정회수를 위한 최적 조건은 온도 100$^{\circ}C$ 이상에서 초기 침출용액 부피에 대하여 약 1/5 정도 농축하는 것이 적절하였다. 이 때 침출용액 대비 약 67.5%의 네오디뮴을 분리하였으며, 농축여액에 잔존하는 나머지 네오디뮴은 옥살산과 반응시켜 전량 회수할 수 있었다.

• 한국재료학회지
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• 제12권10호
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• pp.784-790
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• 2002

For mass product of nanocrystalline ZnO ultrafine powders, self-sustaining combustion process(SCP) and ultrasonic spray combustion method(USCM) were applied at the same time. Ultrasonic spray gun was attached on top of the vertical type furnace. The droplet was sprayed into reaction zone of the furnace to form SCP which produces spherical shape with soft agglomerate crystalline ZnO particles. To characterize formed particles, fuel and oxidizing agent for SCP were used glycine and zinc nitrate or zinc hydroxide. Respectively, with changing combustion temperature and mixture ratio of oxidizing agent and fuel, the best ultrasonic spray conditions were obtained. To observe ultrasonic spray effect, two types of powder synthesis processes were compared. One was directly sprayed into furnace from the precursor solution (Type A), the other directly was heated on the hot plate without using spray gun (Type B). Powder obtained by type A was porous sponge shape with heavy agglomeration, but powder obtained using type B was finer primary particle size, spherical shape with weak agglomeration and bigger value of specific surface area. 9/ This can be due to much lower reaction temperature of type B at ignition time than type A. Synthesized nanocrystalline ZnO powders at the best ultrasonic spray conditions have primary particle size in range 20~30nm and specific surface area is about 20m$^2$/g.

• Membrane and Water Treatment
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• 제3권3호
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• pp.169-179
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• 2012

One of the major limitations in the use of commercial aromatic polyamide thin film composite (TFC) reverse osmosis (RO) membranes is to maintain high performance over a long period of operation, due to the sensitivity of polyamide (PA) skin layer to oxidizing agents, such as chlorine, even at very low concentrations in feed water. This article reports surface modification of a commercial TFC RO membrane (BW30-Dow Filmtec) by covering it with a thin film of poly(vinyl alcohol) (PVA) crosslinked with glutaraldehyde (GA) to improve its resistance to chlorine. Crosslinking reaction was carried out at 25 and $40^{\circ}C$ by using PVA 1.0 wt.% solutions at different GA/PVA mass ratio, namely 0.0022, 0.0043 and 0.013. Water swelling measurements indicated a maximum crosslinking density for PVA films prepared at $40^{\circ}C$ and GA/PVA 0.0043. ATR-FTIR and TGA analysis confirmed the reaction between GA and PVA. SEM images of the original and modified membranes were used to evaluate the surface coating. Chlorine resistance of original and modified membranes was evaluated by exposing it to an oxidant solution (NaClO 300 mg/L, NaCl 2,000 mg/L, pH 9.5) and measuring water permeability and salt rejection during more than 100 h period. The surface modification effectively was demonstrated by increasing the chlorine resistance of PA commercial membrane from 1,000 ppm.h to more than 15.000 ppm.h.

• 대한화학회지
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• 제46권5호
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• pp.444-456
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• 2002

차체의 산화를 방지하기 위하여 희생적 양극을 사용한 산화방지 장치를 개발하였다. 희생적 양극은 철보다 산화 전위가 높은 Mg, Al, Zn으로 만들어 졌고 이것은 차체의 철이나 철합금보다 먼저 산화되어 차체의 부식을 방지한다. 차체 산화방지 장치를 제작하여 철시편을 염산, 질산 및 황산에 대한 방식효과를 시간에 따라 측정하였고 SEM과 XPS를 이용하여 철시편 표면의 방식효과를 분석하였다. 철시편을 산화 방지 장치에 연결하면 산화되어 산성용액 속으로 녹아 들어가는 철의 양이 현저하게 감소하고 철시편 표면의 산화가 방지되며 산화된 철은 $Fe_2O_3$의 산화형태를 가짐을 확인하였다. 따라서 차체 산화방지를 차체에 직접 부착한다면 차체의 부식 및 산화를 효과적으로 방지할 것으로 기대된다.

• 자원리싸이클링
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• 제31권5호
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• pp.26-33
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• 2022

몰리브덴은 소재로 널리 사용되므로 광석 또는 2차자원으로부터 회수가 많은 관심을 끌고 있다. 몰리브데나이트광으로부터 산화제로 NaClO3를 함유한 염산용액에 의한 몰리브데나이트광의 침출에 대해 조사했다. 염산 및 NaClO₃의 농도, 반응 온도 및 시간과 광액밀도가 광석의 침출에 미치는 영향을 조사했다. 산화력이 센 강산용액에서 황화광은 황산이온으로 산화되면서 용해되어 칼슘이온과 gypsum을 형성하여 몰리브덴(VI)의 침출률을 감소시켰다. 최적조건(2.0 M HCl, 0.5 M NaClO₃, 광액밀도 5 g/L, 90, 60분)에서 몰리브덴, 철, 칼슘 및 실리케이트의 침출률은 각각 90, 38, 29 및 67%이었다.

• Membrane and Water Treatment
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• 제9권6호
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• pp.405-419
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• 2018

Persulfates (i.e., peroxymonosulfate and peroxydisulfate) are capable of oxidizing a wide range of organic compounds via direct reactions, as well as by indirect reactions by the radical intermediates. In aqueous solution, persulfates undergo self-decomposition, which is accelerated by thermal, photochemical and metal-catalyzed methods, which usually involve the generation of various radical species. The chemistry of persulfates has been studied since the early twentieth century. However, its environmental application has recently gained attention, as persulfates show promise in in situ chemical oxidation (ISCO) for soil and groundwater remediation. Persulfates are known to have both reactivity and persistence in the subsurface, which can provide advantages over other oxidants inclined toward either of the two properties. Besides the ISCO applications, recent studies have shown that the persulfate oxidation also has the potential for wastewater treatment and disinfection. This article reviews the chemistry regarding the hydrolysis, photolysis and catalysis of persulfates and the reactions of persulfates with organic compounds in aqueous solution. This article is intended to provide insight into interpreting the behaviors of the contaminant oxidation by persulfates, as well as developing new persulfate-based oxidation technologies.

• 한국방사성폐기물학회:학술대회논문집
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• 한국방사성폐기물학회 2005년도 Proceedings of The 6th korea-china joint workshop on nuclear waste management
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• pp.51-59
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• 2005

The long-lived fission product $^{99}Tc$ is present in large quantities in nuclear wastes and its chemical behavior in aqueous solution is of considerable interest. Under oxidizing conditions technetium exists as the anionic species $TcO_4^-$ whereas under the reducing conditions it is generally predicted that technetium will be present as $TcO_2{\cdot}nH_2O$. Technetium oxide was prepared by reduction of a technetate solution with $Sn^{2+}$. The concentration of total technetium and Tc(IV) species in the solutions were periodically determined by separating the oxidized and reduced technetium species using a solvent extraction procedure and counting the beta activity of the $^{99}Tc$ with a liquid scintillation counter. The experimental results show that the rate of oxidation of Tc(IV) in simulated groundwater and redistilled water is about $(1.49{\~}1.86){\times}10^{-9} mol/(L{\cdot}d$) under aerobic conditions, but Tc(IV) in simulated groundwater and redistilled water is not oxidized under anaerobic conditions. Under aerobic or anaerobic conditions the solubility of Tc(IV) oxide in simulated groundwater and redistilled water is equal on the whole.

• 한국재료학회지
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• 제27권9호
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• pp.471-476
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• 2017

In order to improve the high temperature oxidation resistance and lifespan of mat type porous carbon insulation, SiC was coated on carbon insulation by solution coating using polycarbosilane solution, curing in an oxidizing atmosphere at $200^{\circ}C$, and pyrolysis at temperatures up to $1200^{\circ}C$. The SiOC phase formed during the pyrolysis process was converted into SiC crystals as the heat treatment temperature increased, and a SiC coating with a thickness of 10-15 nm was formed at $1600^{\circ}C$. The SiC coated specimen showed a weight reduction of 8.6 % when it was kept in an atmospheric environment of $700^{\circ}C$ for 1 hour. On the other hand, the thermal conductivity was 0.17 W/mK, and no difference between states before and after coating was observed at all.